Note: Descriptions are shown in the official language in which they were submitted.
2092~04
SPECIFICATION
PREVENTION METHOD OF AQUATIC ATTACHING
FOULING ORGANISMS AND ITS APPARATUS
[Technical Field]
This invention relates to a prevention or
control method of aquatic attaching fouling organisms
attaching and breeding on water contact surfaces of
intake passes of power stations, iron foundries, oil
refinery plants, etc, using water such as brine as
cooling water, intake facilities such as screens, and
submerged steel and concrete structures to be submerged
and constructed in sea water such as piers, steel
piles and steel pipe piles, and equipment used for the
method.
[Background Art]
Aquatic organisms inhabiting in water such as
bacterias, seaweeds, shellfishes, etc, attach and breed
on water contact portions of various harbor facilities
such as quays, piers, platform piers, buoys, and
submerged structures such as ships and greatly lower
the functions of such facilities and submerged
structures.
The quantity of cooling water or power
generation water for various intake equipment such as
plant intake passes, intake pipes and screens, which is
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used as cooling water in steam power stations, atomic power
stations, iron foundries, oil refinery plants, etc. or as
power generation water of power stations, ranges from dozens
of thousands of cubic meters to hundreds of thousands of cubic
meter per hour and is extremely great. Therefore, maintenance
management of the intake equipment is of great importance.
The essential points of this maintenance management are
corrosion control of the facilities and control of attachment
10 of aquatic organisms attaching and breeding on the surfaces of
the intake facilities in the same way as in the submerged
structures. Attachment and breeding of the aquatic organisms
are causes for the occurrence of various troubles in the
normal operations of equipments and facilities.
Excellent corrosion prevention engineerings such as
the development of corrosion resistant materials, the progress
in coatings and cathodic protection have been developed and
put into practical applications as corrosion prevention
control means of these submerged structures and intake
facilities.
On the other hand, prevention means against
attachment of aquatic fouling organisms such as marine
creatures have long been employed. In other words, the
following means have been proposed:
(1) adding chlorine or hypochlorites;
(2) coating of anti-fouling paints;
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(3) covering with anti-fouling metals;
(4) formation of chlorine or hypochlorite ions by
brine electrolysisi and
(5) formation of copper ion using a copper anode.
All of these methods are effective as prevention
means against attachment of marine organisms, but they are
anti-fouling means or methods comprising principally the
10 formation of the toxic ions such as chlorine, hypochlorite,
copper, mercury, tin, and there is the possibility that these
toxic ions induce secondary environmental pollution. The
formation and use of these toxic ions require great expenses
for installations for keeping a suitable concentration or
15 density for a long service life and for the maintenance and
management of the installations; but mainly because they use
the toxic ions and may result in environmental destruction
rather than because of expenses, the use of such installations
tends to be inhibited.
Chlorine and hypochlorites can be charged easily,
but the concentration management is difficult. If any
reducing agents or substances exist in water, the consumption
amount of chlorine becomes greater, and the anti-fouling
effect cannot be expected in some cases. A great deal of
labor and expenses are necessary for maintenance and
management of a chlorine
2 Q ~ 2 ~ O ~
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generation apparatus and its concentration management, and
secondary environmental pollution is not avoidable.
Therefore, the use of such compounds is now avoided as much as
possible.
Anti-fouling coatings or paints mostly contain metal
pigments generating toxic ions, and comprise mainly mercury,
mercury compounds, copper, copper alloys and their compounds.
10 Recently, these materials have been replaced gradually by
organic stannous compounds (stannates), but the service life
as the coating is about 2 years. These paints involve the
problem of low durability resulting from impact, wear and
tear. Furthermore, the use of such coatings tends to be
inhibited from the aspects of environmental pollution and
safety in the same way as in the case of chlorine.
Covering with the anti-fouling metals is the method
which applies a covering of copper or a copper alloy to the
submerged area of the structure and controls attachment of the
aquatic fouling organisms by the toxic copper ion slightly
eluting from the surface of copper or the copper alloy.
However, this method needs to cover the entire surface of the
structure and to perfectly insulate the structure (made of
iron steel). (If any defect occurs in the covering metals,
unusual corrosion occurs in the underlayer structure). For
these reasons, the cost of the
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covering work is high. It is one of the anti-fouling
methods based on the toxic ion, and secondary
environmental pollution is not avoidable.
Anti-fouling means of marine organisms on the
wall surfaces of submerged structures, particularly the
intake facilities of plants using large quantities of
brine as cooling water, most widely employ the
formation of chlorine and hypochlorites by electrolysis
of brine or the formation of the copper ion by the use
of a copper anode.
It is known to generate chlorine, particularly
the hypochlorites, by direct electrolysis of brine.
Various attempts have been made to attain higher
economy and higher safety. For example, Japanese
Patent Publication No.(Sho.) 51-41030 (41030/1976)
describes a sea water electrolysis system for
generating hypochlorites. Similarly, Japanese Patent
Publication No.(Sho.) 54-40472 (40472/1979) discloses
an anti-fouling and anti-corrosion method using a
hypochlorite formation apparatus in combination with an
iron ion generating system by sea water electrolysis,
and Japanese Patent Laid-Open No.(Hei.)2-236290
(236290/1990) discloses an anti-fouling system using an
electrode material obtained by applying an insoluble
conductive film and a conductive film made of a highly
conductive material to the submerged structure through
an insulating film in place of a platinized titanium
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and carbon electrode as the conventional hypochlorite forming
anode.
Sea water electrolytic technique using a copper
anode for forming toxic ions has long been known. For
example, Japanese Patent Publication No. (Sho.) 41-5193
(5193/1966) describes a prevention method of aquatic attaching
fouling organisms by D.C. electrolysis by disposing a copper
10 anode and a cathode in the proximity of inner wall surfaces of
sea water intake underdrains or open drains so as to elute the
copper ion by D.C. electrolysis, and Japanese Patent
Publication No. (Sho.) 45-923 (923/1970) describes a method
which disposes a pair of copper electrodes on the inner
surface of a sea water intake pipe and supplies an A.C. or a
current reversible direct current voltage. Similarly,
Japanese Patent Publication No. (Sho.) 43-6374 (6374/1968)
describes a method which prevents attachment of aquatic
fouling organisms by sea water electrolyzed by copper or
copper alloy anode in sea water and adds cathodic protection
means by using the objective structure as the cathode.
Japanese Patent Laid-Open No. (Sho.) 59-9181
(9181/1984) describes a prevention method of aquatic attaching
fouling organisms on the outer surfaces of submerged metal
structures such as ships by applying a plurality of anti-
fouling metals (pricipally copper or copper alloys) on the
submerged areas.
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Anti-fouling means using other metals in place of
copper or using these metals in combination with copper has
5 also been proposed. For example, Japanese Patent Publication
No. ~Sho.) 48-39343 (3g343/1973) discloses a method which
prevents fouling of hulls of ships by covering the hulls with
a zinc layer, uses the zinc layer as the anode while the ships
are at rest by the use of an auxiliary electrode, and uses the
10 zinc layer as the cathode during moving. Japanese Patent
Publication No. (Sho.) 59-40361 (40361/1984) discloses another
method which feeds a D.C. current to an anode made of copper
or a copper alloy and at least one kind of metals selected
from the group consisting of zinc, aluminum, magnesium and
15 iron, and disposed in the proximity, or at an intermediate
part, of an intake port of a cooling pipe system of sea water
or brackish water, which allows the copper ions to be adsorbed
and concentrated by hydroxide colloid of the anode metal, and
thus enhances the anti-fouling effect of the aquatic attaching
20 fouling organisms and at the same time, inhibits the outflow
of the copper ion into sea water.
A method of preventing marine bio-fouling by
generating a combination of A.C. and D.C. currents in order to
elute controlled chlorine and copper ions into sea water is
25 disclosed in Japanese Patent National
- 8 ~ 4
Publication No. (Sho.) 63-502172 (502172/1988) (WO 087/03261).
Anti-fouling means of the aquatic attaching fouling
5 organisms by forming the chlorine and hypochlorite ions by the
electrolysis of sea water or by utilizing the toxic character
of the copper ion, etc. by the electrolysis using copper or
the copper alloy as the anode are effective means, but they
extirpate useful marine organisms in addition to secondary
10 environmental pollution.
According to Japanese Patent National Publication
No. (Sho.) 63-502172 (502172/1988) described above, the action
potential of the marine organisms at the nerve/muscle
interface is disrupted by the use of the A.C., and the
15 possibility of their attachment of the structures is lowered.
This method is said to be the means which controls attachment
of the marine fouling organisms but does not extirpates them.
As a method not involving the formation of the toxic ions,
Japanese Patent Publication No. (Hei.) 1-46595 (46595/1989)
20 discloses a method which, when the metal structures are
constructed by valve metals such as titanium, deposit of a
precious metal oxide catalyst on the surface of the valve
metal, connects the metal structure to the anode of a D.C.
power supply, inhibits the formation of chlorine, generates
25 oxygen and hydrogen gases and prevents deposit of
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marine fouling organisms and scales consisting of
calcium compounds. This method is directed to heat
exchanger pipes made of the precious valve metal such
as titanium. However, it is not industrially
preferable to cover the surface of facilities, which
are great both in the quantity and in the number, or
the surface of the structures which are exposed to
marine tidal currents changing incessantly, by the
oxide catalyst coating valve metal.
As described above, various anti-fouling means
for preventing attachment of the aquatic attaching
fouling organisms inhabiting and growing on the
submerged areas of the marine structures have been
developed, but none of them are entirely satisfactory.
In other words, they involve the problems that the
toxic ions are generated, secondary environmental
pollution may be induced, maintenance management of the
equipments is not easy, the running cost is high, and
even useful aquatic organisms are extirpated.
For example, intake facilities of power
stations, etc, introducing large quantities of sea
water as cooling water have the problem of getting rid
of aquatic fouling organisms expanding over one
thousand meters. At present, the removing operation is
mechanically carried out by a manual operation (workers
or divers) or using robots. In addition to its low
removal efficiency, this method involves a large number
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of safety problems, requires an enormous removal cost, and
needs a disposal and waste site of the marine organisms thus
removed. Therefore, not only economical but also industrial
losses are very large.
[Summary of the Invention]
The object of the present invention is to provide a
prevention and control method of aquatic attaching fouling
10 organisms having high efficiency and high economy and its
equipments, which do not reply on the generation of chlorine
and toxic ions, are free from secondary environmental
pollution and moreover, do not extirpate the aquatic
organisms.
The inventors of the present invention have paid a
specific attention to the fact that attachment and habitation
of marine organisms can be hardly observed on the surface of
an electrode functioning as an anode in conventional cathodic
protection which has been applied to corrosion control of
marine structures such as hulls of ships, harbor facilities,
etc., by sea water, and have completed the present invention
by utilizing and applying this phenomenon to intake facilities
for which anti-fouling measures of marine organisms has been
very difficult. The inventors of the present invention have
realized further that this method can be applied to other
marine structures, and intake facilities and submerged
structures in fresh
,~
water and brackish water, and have completed the present
lnventlon.
Fundamentally, the present invention is based on the
observation that attachment and breeding of aquatic organisms
can be scarcely observed or are drastically controlled on
active dissolving portions by anodic electrolysis of metals
selected from transition metals for generating non-poisonous
10 ions, without using metals generating chlorine or toxic ions.
Species and breeding seasons of aquatic organisms
are different depending on seasons and sites, as will be
described in more detail next. The marine organisms that
cause problems in sea-water, for example, marine structures
15 and marine intake facilities, are mussels, barnacles, sea
squirts, oysters and seaweeds such as sea lettus and green
laver. Particularly in the case of intake facilities (intake
passes) of power stations, mussels account for 80% of the
fouling organisms and barnacles do the rest, and the
20 prevention of attachment of these marine organisms is a great
technical problem. Generally, their attachment can be hardly
observed at low temperature in winter season. They attach and
grow in a warm season from spring to summer, and breed from
fall to winter, but new attachment is not observed. The
25 aquatic attaching fouling organisms cannot attach unless
bacteria and slimes attach to a substratum.
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Therefore, prevention control of their attaching can be
accomplished by preventing the attachment of these bacterias
and slimes to the substratum, or even if they do, by
preventing in advance the growth of their larvae.
As described above, the present invention does not
relate to the prevention and control method of the aquatic
attaching fouling organisms by their extinction by the toxic
10 ions but prevents and controls the method of their attachment.
In other words, the gist of the present invention
resides in the following points.
(1) A prevention and control method of aquatic attaching
fouling organisms comprising: covering attaching portions of
aquatic fouling organisms on the surfaces of submerged
structures or intake facilities with a plurality of mutually
insulated metallic covers made of iron, magnesium, aluminum or
their alloys through an insulating material and a cushion
material; using the metallic covers as electrodes,
respectively; composing an electric circuit using a pair of
the metallic covers facing each other; connecting the electric
circuit to a D.C. power supply having a current reversal
function; supplying a current between both of the electrodes
either continuously or intermittently; and reversing a current
polarity so that when one of the metallic covers is an anode,
the
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surface of the metal constituting the metallic cover is
dissolved and activated, and attachment of the aquatic fouling
organisms is controlled or prevented.
(2) A prevention and control method of aquatic attaching
fouling organisms comprising: covering attaching portions of
aquatic fouling organisms on the surfaces of a submerged
structure with a metallic cover made of iron, aluminum,
10 magnesium or their alloys through an insulating material and a
cushion material; connecting the metallic cover to a positive
pole of a D.C. power supply and using it as an anode;
connecting the submerged structure to a negative pole of the
D.C. power supply to use it as a cathode and to form an
electric circuit; and supplying a current between the cathode
and the anode either continuously or intermittently so as to
prevent or control the attachment of the aquatic fouling
organisms to the surface of the anode metallic cover by
dissolving and activating the surfaces of the metallic cover.
(3) A prevention and control method of aquatic attaching
fouling organisms comprising: covering attaching portions of
aquatic fouling organisms on the inner surfaces of an intake
facility other than its bottom surface with a plurality of
mutually insulated metallic covers made of iron, magnesium,
aluminum or their alloys through an insulating material and a
cushion material; connecting the metallic covers to a
A
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positive pole of a D.C. power supply and using them as
an anode; disposing iron or an iron alloy material on
the bottom surface of the intake facility and
connecting it to a negative pole of the D.C. supply to
use it as a cathode to form an electric circuit; and
supplying a current between the cathode and the anode
either continuously or intermittently so that the
surfaces of the metals constituting the metallic cover
are dissolved and activated, and attachment of the
aquatic fouling organisms to the surfaces of the
metallic cover is controlled or prevented.
The structures to which the present invention
are directed are submerged structures and intake
facilities in sea water, fresh water and brackish
water.
Here, the term "submerged structures"
represents various harbor facilities constructed in
water such as quays, piers, platform piers and buoys
and ships, and made primarily of iron steel materials
and concrete materials.
The term "intake facilities" represents intake
passes and intake pipes for cooling and power
generation, and structures using such intake facilities
are various factories and plants such as steam power or
water power stations, iron foundries, oil refinery
plants. The cross-sectional views of the surfaces of
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these intake facilities are rectangles, circles, ovals,
squares, etc, and their shapes are arbitrary.
According to the present invention, the wall
surfaces of these submerged structures and intake facilities,
on which the aquatic fouling organisms are likely to attach,
are covered with mutually insulated metallic covers made of
iron, aluminum, magnesium or their alloys, through an
10 insulating material and a cushion. A synthetic rubber such as
neoprene and silicon rubber and plastics such as PVC,
polyethylene and polyester are used as the insulating
material. Blistered polyethylene sheets, blistered
polyurethane sheets, etc, are used as the cushion.
One of these materials may be used as the insulating
material and the cushion. A synthetic rubber or a plastic of
10 mmt or more is used as this insulating-cushion material.
The coating of the metallic covers is fixed to the surfaces of
the submerged structures by the use of customary means as
insulating bolts and adhesives.
A pair of these metallic covers facing each other
are used as electrodes so as to form an electric circuit, and
are connected to a D.C. power supply having a current reversal
function. The current is supplied between both electrodes
either continuously or intermittently, and the current
polarity is reversed so that when one of the metallic covers
is the anode, the
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.
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surface of the metal constituting the metallic covers is
dissolved and activated and attachment of the aquatic fouling
organisms is controlled or prevented. The electric circuit
formed hereby may have a combination function with A.C.
To reduce the time during which the metallic cover
is the cathode, the reversal interval of the current is
preferably carried out at the interval of 10 seconds to 60
10 minutes.
When the current is supplied intermittently, an
interval between the current supply and the non-supply is
preferably shortened. Generally, this gap is preferably from
10 seconds to 60 minutes. When the current is supplied for 4
15 hours per day, this 4 hours' time is preferably divided as
finely as possible when supplying the current.
When the structure is the submerged structure, the
portions of the structures to which the aquatic fouling
organisms attach are covered with the metallic cover made of
iron, aluminum, magnesium or their alloys through the
insulating material and the cushion material in the same way
as described above. The metallic cover is connected to the
positive pole of the D.C. power supply and is used as the
anode while the structure is connected to the negative pole of
the D.C. power supply so as to form the electric circuit. The
current is supplied between the
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anode and the cathode either continuously or intermittently,
so that the surface of the metallic cover can be dissolved and
activated and attachment of the aquatic fouling organisms to
the surface of this anode metallic cover can be prevented or
controlled. In this case, water functions as an electrolyte.
As a result, attachment of the aquatic fouling organisms to
the surface of the metallic cover in contact with water is
10 controlled and since the current flows into the submerged
structure, surrounding corrosion can be controlled. The
electric circuit in this case need not always have the
polarity reversal function.
Since the electric circuit is formed between the
anti-fouling metallic cover and the submerged structure in
this case, their direct short-circuit must be avoided.
Therefore, a sheet-like product or molded product having a
similar shape to the outer shape of the submerged structure is
preferably used as the anti-fouling metallic cover.
A protective cover is applied in some cases to
water-line portions of the submerged structure such as piers
for the purpose of corrosion protection. In this case, the
metallic cover described above may be applied to the submerged
structure by removing the corrosion protection cover of the
outermost layer applied below the waterline or below water,
through the insulating material and the cushion in place of
the corrosion
A
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protection cover. In this way, the submerged structure is
protected by both the above prevention control method of the
aquatic attaching fouling organisms and the protective cover.
Generally, sand, mud, etc, are likely to stay at the
bottom portions of the intake facilities and since these
portions have insufficient supply of oxygen (air), the aquatic
fouling organisms can hardly grow up at such portions. In
10 such a case, the portions of the intake facilities at which
the aquatic fouling organisms attach, other than the bottom
surface, are covered with the insulated metallic cover through
the insulating material and the cushion material, and this
metallic cover is connected to the positive pole of the D.C.
power supply and is used as the anode. On the other hand,
iron or its alloy is disposed on the bottom surface of the
intake facilities, is connected to the negative pole of the
D.C. power supply and is used as the cathode. These anode and
cathode together constitute an electric circuit, and the
current is supplied between them either continuously or
intermittently so as to dissolve and activate the surface of
the metal constituting the metallic cover and to prevent or
control the attachment of the aquatic fouling organisms. The
electric circuit obtained in this case need not always have
2~ the current reversal function.
, ~
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In the present invention, active dissolution
of the electrode due to the anode current prevents or
controls attachment of the aquatic fouling organisms.
Therefore, there is an anode current density which is
suitable for the prevention or control. Though the
anode current density is preferably great, it is
preferably not more than 500 mA/m2 (0.5 A/m2) from the
economical and industrial aspects, more preferably from
40 to 500 mA/m2 (0.04 to 0.5 A/m ) and further
10preferably, 150 to 300 mA/m2 (0.15 to 0.3 A/m2). It is
also preferred to regulate the anode current density,
either regularly or irregularly, in accordance with the
species or active living time of the aquatic fouling
organisms.
15An apparatus preferably used for the
prevention method of aquatic fouling organisms
according to the present invention comprises a multi-
layer structure fitted to attaching portions of aquatic
fouling organisms on the surfaces of submerged
structures or intake facilities, and comprising an
insulating material, a cushion material and a metallic
cover made of iron, aluminum, magnesium or their
alloys; and a D.C. power supply capable of supplying a
current between the metallic covers or between the
metallic cover and the submersed structure; or
comprises a multi-layer structure fitted to attaching
portions of aquatic fouling organisms on the inner
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surfaces of intake facilities other than its bottom
surface, and comprising an insulating material, a
cushion material and a metallic cover made or iron,
aluminum, magnesium or their alloys; iron or its alloy
member disposed on the bottom surface of the intake
facility; and a D.C. current supply capable of
supplying a current between the metallic cover and the
iron or iron alloy member.
As the prevention apparatus against the
aquatic attaching fouling organisms, an apparatus the
D.C. power supply of which constitutes an electric
circuit having a current reversing function, an
intermittent current supply function or a combination
function with A.C. is used preferably.
lS The present invention uses iron, aluminum,
magnesium and their alloys, the dissolved ions of which
have hardly any toxicity or are said to be harmless, as
the anode in water. Therefore, the aquatic fouling
organisms hardly attach to the surface of the metal,
and even when they do, their adhesive strength to the
metal surface is very low and they easily fall off from
the metal surface. Moreover, the formation of the
chlorine gas due to electrolysis hardly occurs even in
the case of sea water, and the formation of the oxygen
gas and the hydrogen gas is hardly observed, either.
The reason why attachment of the aquatic
fouling organisms is restricted by dissolution of the
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anode metal by the D.C. electrolysis without the
formation of such toxic ions and gases has not yet been
clarified sufficiently, but is assumed as follows:
Namely, when a D.C. voltage is loaded between the anode
metal and the cathode metal, active dissolution of the
anode metal occurs to fall short of attaching
conditions of the aquatic fouling organisms, so that
these organisms lose their attaching abilities.
Brief Description of the Drawings:
Fig. 1 is a graph showing the relation between
an anode current density of a current which is constant
throughout the year, the quantity of marine deposited
organisms on the surface of the anode, an anode
corrosion rate and an anode potential;
Fig. 2 is a graph showing the relation between
an anode current density, the quantity of marine
deposited organisms, an anode corrosion rate and an
anode potential, by season;
Fig. 3 is a graph showing the relation between
the quantity of marine deposited organisms and a
critical anode current density throughout the year and
by season;
Fig. 4 is a perspective view showing an
embodiment of an anti-fouling apparatus for aquatic
fouling organisms according to the present invention
which is installed in a box culvert type intake pass;
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Fig. 5 is a sectional view of the anti-fouling
apparatus for aquatic attaching fouling organisms shown
in Fig. 4;
Fig. 6 is a side view of a portion A - A' in
Fig. 5;
Fig. 7 is a diagram of distributing lead wires
of the anti-fouling apparatus of marine organisms shown
in Fig. 4;
Fig. 8 is a time chart showing an example of
an operation cycle of a current flow;
Fig. 9 is a sectional view showing the anti-
fouling apparatus for marine organisms according to
another embodiment of the present invention;
Fig. 10 is a time chart showing an example of
the operation cycle for the current supply;
Fig. 11 is a perspective view showing the
state where the present invention is applied to base
steel pipe piles of a pier;
Fig. 12 is a sectional view showing an example
where the anti-fouling apparatus for marine organisms
is fitted to one base steel pipe pile shown in Fig. 11;
Fig. 13 is a sectional view showing another
example where the anti-fouling apparatus for marine
organisms is fitted to one base steel pipe pile;
Fig. 14 is a side view showing the state where
the present invention is applied to the hull of a ship;
and
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Fig. 15 is a sectional view of Fig. 14.
Best Mode for Carrying Out the Invention:
Hereinafter, the present invention will be
explained definitely with reference to embodiments
thereof, but the invention is in no way limited by
these embodiments.
Embodiment 1
Experiments were carried out for the relation
between an anode current density, the species of
aquatic fouling organisms and the quantity of their
attachment when active dissolution was effected using
an iron steel as an anode.
An iron steel sheet (having the inside with an
insulating cover~ of 3.2 t x 350 w x 450 Lmm was
connected to a positive pole of a D.C. power supply and
was used as an anode inside a natural marine zone
facing Suruga Bay, Shizuoka Prefecture, as a
substantially average sea area in Japan, and another
iron steel member disposed separately was used as an
opposed cathode. A constant current was supplied
between the cathode and the anode so as to examine the
conditions of attachment of marine organisms to the
surface of the anode iron steel material, a consumption
rate of the anode and an anode potential.
The anode current density was set to 14 stages
from no-current for control to 3,000 mA/m2 (i.e. 0, 10,
20, 30, 50, 100, ..., 3,000 mA/m2). The period of the
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current flow started from early winter (toward the end
of December) during which the marine organisms were
said to be non-active, passed through active seasons
(spring to early summer), breeding and best growing
season (early summer to early fall) and ended in
moderate growing season (early fall to early winter)
for about one year.
Fig. 1 shows the quantity of the marine
organisms, the anode corrosion rate and the anode
potential-anode current density relation after the
supply of power for about a year. In the drawing, a
solid line represents the quantity of the aquatic
fouling organisms for each anode current density, a
dotted lines represents anode corrosion rate, and a
dash line represents the anode potential.
As shown in Fig. 1, the attaching quantity of
the marine organisms decreased with the increase of the
anode current density, and dropped drastically when the
anode current density exceeded 40 to 50 mA/m2.
Furthermore, when the anode current denslty exceeded
100 mA/m , the attaching quantity of the marine
organisms was below 0.5 kg/m2, which could be
substantially neglected, and was close to O at 200
mA/m .
On the other hand, the anode corrosion rate
was naturally greater than 0.1 to 0.2 mm/Y of a normal
corrosion rate, and became greater with a higher
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current. When the current exceeded 500 mA/m2, the
anode corrosion rate became 3 times that of natural
corrosion and drastically increased.
As is obvious from the explanation given
above. the anode current density is up to 500 mA/m , is
from 40 to 500 mA/m from the industrial and economical
aspects as well as from the aspect of environmental
preservation, and is most preferably 150 to 300 mA/m2.
The anode potential somehow got to a noble
potential when the anode current density exceeded 500
mA/m2, but was below -600 mV even at 3,000 mA/m2 and
was hardly polarized from the normal potential of the
steel. In other words, in comparison with 1.0 V (SCE)
as the evolution potential of chlorine in sea water, it
was by far based and the occurrence of chlorine could
not at all be considered.
When the relation between the deposited marine
organisms and the anode current density was examined in
further detail, large quantities of various organisms
such as mussels, barnacles, sea squirts, tube worms,
etc, attached to all the surfaces of the electrode
without a current, and they grew to a thickness of 10
to 20 cm. When the current density was less than 40
mA/m , large quantities of barnacles and sea squirts
attached. Though attachment of mussels could be
observed partially, this attachment dropped drastically
or became nil at the current density of 40 to 50 mA/m2,
20923Q I
- 26 -
and barnacles, sea squirts and tube worms attached
locally. When the current density was more than 100
mA/m2, attachment of almost all the marine organisms
could not be observed, and matured lavae of barnacles
were observed spottedly or seaweeds could be observed.
Also, yellow brown products could be observed. These
products could be easily removed when rubbed with
fingers, and the steel surface having a metal luster
could be observed below these products.
Embodiment 2
Activity of the marine organisms exhibits a
seasonal change. For example, the species and
attaching quantity of these marine organisms attaching
to fixed structures such as intake passes and submerged
structures change with seasons, that is, four seasons,
months, water temperatures, and so forth, and their
habits also change. In this embodiment, therefore, the
attaching conditions were tested by dividing a year
into four periods (first period: the last third of
December to the second third of March, second period:
the last third of March to the second third of June,
third period: the last third of June to the second
third of September, fourth period: the last third of
September to the second third of December), and the
attaching conditions in each three month's period were
examined because the experiments were carried out for
full one year in Embodiment 1. The sea water
2~92~04
temperatures were 14.0 ~C for the first period, 16.6~C
for the second period, 24.3 ~C for the third period and
18.8 ~C for the fourth period, and the seasons
corresponded to these water temperatures, respectively.
The results of the experiments were tabulated
in Fig. 2. In this diagram, a solid line represents
the attaching quantities of each period (season), a
dotted line represents the anode consumption rate and a
dash line does the anode potential.
The attaching quantity of the marine organisms
decreased with an increasing anode current density, and
this tendency resembled that of the experiment for full
one year shown in Fig. 1. The attaching quantity of
the marine organisms was smaller in each period even in
the case of the non-supply of the current in comparison
with the case of the supply of the current, because a
new steel material was charged in each period.
When evaluation was made for each period, it
was found that the attaching quantity of the marine
organisms was 0.3 to 0.4 kg/m2 even when the current
was not supplied, in the first winter period (average
water temperature = 14.0 ~C), and this value was at a
negligible level.
In the second period as the active attaching
season when water started to warm (average water
temperature = 16.6 ~C~, attaching of mussels was
accelerated, and barnacles, sea squirts and seaweeds
2~ 3~
- 28 -
started attaching. The attaching quantities of these
marine organisms to the anode surface decreased with
the increase in the anode current density, and when the
density exceeded 40 to 50 mA/m , the attaching quantity
decreased drastically, and could be substantially
neglected at more than 120 mA/m as the quantity
dropped to not more than 0.2 kg/cm .
Attachment, growth and reproduction of the
marine organisms became remarkable irrespective of
their species in the third period as the hot summer
period (average water temperature = 24.3 ~C). In this
period, new attachment of mussels could be hardly
observed but attachment of barnacles and sea squirts
became greater. The attaching quantities of the marine
organisms were the greatest in this period in which the
growth and reproduction of the marine organisms were
vigorous. Although the attaching quantities decreased
with the increase in the anode current density, the
attaching quantities were some multiples of other
seasons at a low current density. The attaching
quantity was not more than 0.5kg/m2 at 100 mA/m2, and
could be neglected substantially at more than 130 mA/m2
because the quantity was not more than 0.2 kg/m2.
Since new attachment of the marine organisms
decreased in the fourth period (average water
temperature = 18.8 ~C) where activity of the marine
organisms was stable, the overall attaching quantity
209~304
- 29 -
dropped and the attaching tendency was similar to that
of the second period. In this period, attachment of
barnacles and white sea squirts was observed to some
extents but new attachment of mussels was hardly
observed.
On the other hand, the anode consumption rate
was represented by a corrosion rate (mm/Y~, and the
tendency was similar to a corrosion tendency of the
year round experiment. In any case, the anode
consumption rate became great when the anode current
density exceeded 500 mA/m2, and this was not
advantageous from the industrial and economical aspect
and also from the conservation of environment.
The most optimum anode density for limiting
the corrosion rate to not more than 0.5 mm/Y and
minimizing the attaching quantity of the marine
organisms was 100 to 400 mA/m .
The anode potential, too, was similar to that
of the year round experiment, and the generation of
chlorine could not be believed as described in
Embodiment 1.
Embodiment 3
A critical anode current density for limiting
the attaching quantity of the marine organisms to less
than 1.0 kg/m2, less than 0.5 kg/m2, less than 0.2
kg/m2 and less than 0.1 kg/m2 in the year round
~092304
- 30 -
experiment and the first to fourth periods was
measured, and the result was shown in Fig. 3.
As the attaching quantity of these marine
organisms was brought closer substantially to zero, the
critical anode current density had to be increased. To
limit the attaching quantity to less than 0.2 kg/m2
(generally, below 1/100 of the attaching quantity 30 to
40 kg/m of the marine organisms under the natural
state), the anode current density had to be at least
140 mA/m in the year round experiment, but in
accordance with the periods, the anode current density
was less than 20 mA/m2 in the first period, 110 mA/m2
in the second period, 130 mA/m in the third period and
180 mA/m in the fourth period. One of their values in
four periods was higher than the anode current density
in the year round experiment, but these values were 110
mAjm on an average. In other words, the current could
be reduced to 80% of the constant current through the
year round.
Embodiment 4
Fig. 4 is a perspective view showing an
embodiment of a prevention apparatus against marine
attaching organisms according to the present invention
installed in a box culvert type intake facility, Fig. 5
is a sectional view of the apparatus shown in Fig. 4,
and Fig. 6 is a side view of a portion A - A' in Fig.
5. In Figs. 4 to 6, reference numeral 1 denotes a
2092~04
- 31 -
panel shape laminator (electrode); 2 is an insulating
frame (electrode support); 3 is fixing means (bolts);
and 4 is marine intake facilities (cooling water intake
pass). In Fig. 4, an arrow represents a water flow
direction. In Figs. 4 to 6, a D.C. power supply for
supplying a current to each panel shape laminator is
not shown. The inner wall portion of this cooling
water intake pass 4 had a width of 2.4 m, a height of
3.0 m and a length of 200 m.
As shown in Figs. 4 to 6, a plurality of panel
shape laminators 1 serving as the electrodes were
fitted to all the inside wall surfaces (objective area
= 180 m ) of the cooling water intake pass 4 other than
its bottom surface. The shape of cross-section of the
inside wall surfaces of this cooling water intake pass
4 was rectangular as shown in Fig. 5.
Each panel shape laminator 1 consisted of a
multi-laminator (by bonding a back surface insulator
and a cushion) of an SS 400 steel sheet, and had a
width of 0.85 m, a length of 1.8 m and a thickness of
1.6 mm.
The electrode support 2 (width: 0.1 m, length:
4 m) made of FRP was used for the insulation between
the panel shape laminators 1 and fixed support bolts 3
of a resin cure-and -bury type (tradename: "Chemical
Anchor") were used for fixing. A recess was formed on
the surface of this FRP electrode support 2 and was
2092304
filled up with a self polishing anti-fouling paint to
prevent attachment of the marine organisms.
A definite fixing method is as follows. Each
panel shape laminator 1 was inserted and clutched into
a support groove of the FRP electrode support 2 fixed
to the wall surface of the cooling water intake
facility using the chemical anchor in consideration of
the retention of the strength to the flow velocity and
uniform consumption of the anode (panel shape
laminator) 1. Furthermore, to prevent vibration of the
panel shape structure 1, the fixed supporting bolts 3
were applied at the center of the laminator 1 in its
longitudinal direction with 2 spots between them.
Fig. 7 shows a lead wiring figure of this
prevention apparatus against the marine attaching
organisms. Reference numerals are the same as those
used in Fig. 4. Reference numeral 5 represents a
connecting wire, 6 is a D.C. circuit, 7 is a D.C. power
supply, 8 is an A.C. circuit,, 9 is a control circuit,
and 10 is a control box (concentric control apparatus).
The D.C. circuit 6 was connected to the D.C.
power supply 7 using an intake pass cable fitted to the
back of each panel shape structure as the connecting
wire 5 and using a CV cable for the underground
portion. The panel shape laminators 1 on the facing
inside wall surfaces form a pair and the D.C. circuit
6 was connected to the D.C. power supply 7 so that the
2092304
- 33 -
panel shape laminators function as the anode and the
cathode, respectively. The D.C. power supply 7 was of
a full wave rectification type, has output power of DC
20 V x 80 A, and selectively supplied power in
accordance with the instruction from the control box 10
having the concentric control function of current
reversal and intermittent current supply. The control
box 10 normally received power of AC 600 V, 3 ~,
converted it to 200 V, 3 ~ and supplied it to the D.C.
power supply 7. At the same time, the control box 10
controlled the operation of the D.C. power supply 7 by
the concentric control function, and monitored the
attaching state of the marine organisms on the wall
surfaces of the intake pass through a monitor. To
reduce the power loss due to the voltage drop of the
D.C. circuit 6 and the material and work costs of the
pipings and lead wires, the D.C. power supply 7 was
divided into five segments and were disposed near the
cooling water intake pass 4 as shown in the drawing.
Five D.C. power supplies 7 were disposed as one circuit
for each of these segments, and each of the D.C.
supplies 7 were concentrically managed by the control
box 10.
The current was supplied by dividing one hour
into three cycles by the polarity reversal mechanism
assembled in the D.C. power supply. Fig. 8 shows a
time chart as an example of this current supply
2092304
- 34 -
operation cycle. In this operation cycle, the current
supplied is 54 A (0.3 A/m2) and the operation was
carried out for about 50 days from the spring season as
the reproduction season of the marine organisms. As a
result, attachment of the marine organisms on the
surface of the panel shape laminators could be hardly
observed, and the surface exhibited a blackish brown
color. Thereafter, the current was reduced to 5.4 A
(0.03 A/m2), but attachment of the marine organisms was
not observed even after the passage of 70 days, though
attachment of seaweeds was partly observed. In
contrast, in similar cooling water intake passes not
subjected to any anti-fouling treatment, marine
organisms such as seaweeds, barnacles, mussels, etc,
attached to the surfaces of the intake passes, and were
observed growing day by day in this season.
During the operation, the anode potential of
the panel shape structure was -600 to -710 mV (SCE) and
did not reach 1.1 V (SCE) which was the chlorine
generating potential in sea water, and chloride was not
generated. The cathode potential of the panel shape
laminator was a less noble potential than -900 mV, and
was completely corrosion-proofed. Though attachment of
the marine organisms to these panel shape laminators
due to the electrolytic reaction was observed, they
could be removed easily by current reversal. The
electrolytic voltage was 2.0 to 4.0 V. When the
2Q32~
- 35 -
current was reduced to 5.4 A, the voltage showed 1.0 to
1.5 V.
Embodiment 5
Fig. 9 is a sectional view showing the
prevention apparatus against marine organisms according
to another embodiment of the present invention. In the
drawing, like reference numerals are used as in Figs. 4
to 6, and reference numeral 11 denotes a cathode
material.
In this apparatus, a plurality of panel shape
laminators 1 as the anode were fitted to all the inside
wall surfaces of the cooling water intake pass 4 other
than its bottom surface in the same way as in
Embodiment 4 (objective area: 180 m2). A cathode
material 11 made of a steel was disposed on the inside
wall bottom surface of the cooling water intake pass 4.
An electric circuit was constituted using a
plurality of panel shape laminators as the anode and
the cathode material 11 as the cathode, and a current
was supplied under the same condition as that of
Embodiment 4. In other words, the current was 54 A
(0.3 A/m2), and ON/OFF of the current was repeated.
One cycle consisted of ON and OFF for 30 minutes,
respectively, and the operation of 24 cycles/day was
carried out. This time chart is shown in Fig. 10.
As a result, attachment of the marine
organisms could be hardly seen on the surface of the
2092~Q ~
- 36 -
panel shape laminators in the same way as in Embodiment
4 even after the passage of 50 days, and the surface
remained blakish grown. The surface area of the
cathode was extremely smaller than that of the anode
panel shape laminators and was under the over-
protection state. Therefore, a coating consisting of
calcium and magnesium was hardly deposited to the
cathode surface but peeled off, and attachment of the
marine organisms was hardly observed.
Embodiment 6
Fig. 11 is a perspective view showing another
embodiment of the present invention applied to steel
pipe piles of substructures of piers. Fig. 12 is a
sectional view of the steel pipe pile portions of the
substructure. This embodiment was directed to the
steel pipe piles of one block of the piers, and one
block had a planar shape of a length of 36 m and a
width of 12 m, the outer diameter of the steel pipe
piles of the substructure was 800 mm, and these piles
were disposed in an arrangement of 5 rows by 4 columns.
Fig. 11 shows the lead wires in magnification.
In Figs. 11 to 12, reference numeral 12
denotes a marine structure (steel pipe piles of the
pier), 13 is a metal member (anode), 14 is a cathode
terminal, 15 is a connection box for electrodes, 16 is
a D.C. lead wires, 17 is a distribution box, 18 is a
D.C. power supply, 19 is an upper structure of the
2092~
- 37 -
pier, 20 is an insulation/cushion material, 21 is a
corrosion protecting material, 22 is a corrosion
protecting cover, and 23 is fixing means. Symbol
H.W.L. represents a high water level line, and L.W.L
does a low water level line.
The steel pipe piles 12 were provided with the
corrosion protecting material 21 such as a petrolatum
paste, petrolatum tape and a plastic blistering
material, and with the corrosion protecting cover 22
made of FRP with the tidal zone being the center.
As shown in Fig. 12, a part of the FRP
protecting cover 22 as the outermost layer of this
corrosion-proof coating, that is , the marine organisms
attaching portion, was removed, and a steel sheet 13
(metal member) having a thickness of 2.3 mmt was wound
through the insulation/cushion material 20, and was
fastened and fixed to the steel pipe piles 12 by the
fixing means 23.
To use the steel sheet 13 as anode, an
electric circuit contact was disposed on the back of
the steel sheet and insulation coated wires were
fitted. The lead wires were extended to the connection
box 15 for electrode provided on the superstructure of
pier and were connected to the positive pole of the
D.C. power supply 18. On the other hand, another lead
wire was connected to the steel pipe piles 12, was
taken into the connection box 15 for electrodes, and
2092~04
- 38 -
was connected to a negative pole of the D.C. power
supply 18.
In the steel pipe pile pier shown in Fig. 11,
cathodic protection by galvanic aluminum alloy anodes
was applied to the steel pipe piles which was always
kept below water surface. Therefore, the prevention
apparatus against the marine organisms in this
embodiment was disposed so as to cover the portion 1 m
below L.W.L up to H.W.L.
This prevention apparatus against the marine
organisms was practiced for 20 steel pipe piles of one
block, and corrosion protective covering was applied to
other blocks as usual and cathodic protection was
applied to the portions kept always below the sea water
level. The work was finished in the fall season, and
the supply of the current was started in early spring
when the marine organisms started their activity.
Observation was made after about a year through the
active periods of spring, summer and fall.
The continuous current was supplied at a rate
of 50 mA/m2 in the early active season of the marine
organisms, and at rates of 250 mA/m2 in April to May,
200 mA/m2 in June to August, 100 mA/m2 in September, 50
mA/m2 in October, and 20 mA/m2 in November,
respectively, but no current was supplied during
December to February.
2092~04
- 39 -
The ON/OFF supply of the current in a 30
minutes' unit with a constant current quantity per day
was applied to part of the steel pipe piles during
April and May as the best reproduction season.
As a result, attachment of the marine
organisms in a thickness of about 15 to 20 cm was
observed on the steel pipe piles not using the
prevention apparatus of this embodiment below and near
the water level, but in the case of the steel pipe
piles using the prevention apparatus, attachment of
slimes, seaweeds or extremely small shellfishes was
observed in a part of the steel pipe piles. When the
attaching quantities of the marine organisms were
measured, the values were 40 to 60 kg/m2 for the former
and not more than 0.5 kg/m2 for the latter, which was
below 1/100 of the prior art.
Embodiment 7
Fig. 13 is a sectional view showing the state
where the present invention was applied to the steel
pipe piles for substructures. In this drawing, like
reference numerals are used to identify like
constituents as in Fig. 12. Reference numeral 201
denotes a cushion material and 202 does an insulating
material. Since anti-fouling coating was not applied
to the steel pipe piles 12, a 2.3 mm-thick steel sheet
(metal member) 13 was applied to the steel pipe piles
12 through the insulating material 202 and the cushion
209230~
- 40 -
material 201 up to a splash zone above H.W.L. In this
embodiment, too, in order to use the steel sheet 13 as
the anode, the electric contact bonding part was
disposed on the steel sheet, and an insulating coating
lead wire was fitted, was guided to the connection box
15 provided on the superstructure of pier 19 and was
connected to the positive pole of the D.C. power supply
18. On the other hand, another lead wire was connected
to the steel pipe piles 12, was taken into the
connection box 15 and was connected to the negative
pole of the D.C. power supply 18.
An experiment was carried out using this
prevention apparatus against the marine organisms in
the same way as in Embodiment 6. As a result, although
attachment of slimes, seaweeds and extremely small
shellfishes was observed at a part of the steel pipe
piles, the attaching quantity was extremely small.
Embodiment 8
Fig. 14 is a side view showing another
embodiment of the present invention applied to the ship
hull, and Fig. 15 is its sectional view.
In Figs. 14 and 15, like reference numerals
are used to identify like constituents as in Fig. 12.
Reference numeral 24 denotes a screw propeller, 25 is a
rudder, and 26 is an insulation keel, and symbol W.L
represents a draught line.
20923~
- 41 -
In this embodiment, the steel sheet (metal
member) 13 was fitted through the insulation/cushion
material 20 in place of an anti-fouling anti-corrosion
paint applied to the ship hull (marine structure) 12.
The steel sheet 13 and the insulation/cushion material
20 were produced in advance into a unistructure. To
fit this unistructure to the ship hull 12, an adhesive
was applied to the insulation/cushion material 20, and
fastening was made by the use of stud bolts (fixing
means) 23 at necessary portions. The head of each stud
bolt 24 was shaped by a streamline cap so as to
minimize the water contact resistance.
When the experiment was carried out using this
prevention apparatus against the marine organisms,
attachment of slimes and extremely small shellfishes
was observed partly on the ship hull after the passage
of six months, but the attaching quantity was extremely
small.
The foregoing embodiments of the invention
represent the case of the marine structures and sea
water intake facilities constructed in sea brine, but
the present invention can of course be applied in the
same way to submerged structures constituted in fresh
water and brackish water and to intake facilities of
power generation plants.
Industrial Availability:
209230'~
- 42 -
As described above, the present invention can
industrially and economically prevent or control
aquatic attaching fouling organisms by controlling the
current density of the anode as the anti-fouling object
in accordance with the life mode of aquatic fouling
organisms. Particularly, the method of the present
invention is not the method which eliminates the marine
organisms by generating toxic metal ions or forming
chlorine and hypochlorites, but is the prevention
method of the attaching fouling organisms on the basis
of active dissolution of intoxic metals. Since the
anode current density for limiting the quantity of
deposition of the aquatic fouling organisms to an
allowable value is now clarified, the operation
management becomes easy, and the service life of the
anode can be estimated.
Furthermore, the reduction of power
consumption and a further extension of the service life
of the anode become possible by regulating the anode
current density in accordance with the seasons, that
is, in accordance with activity (active and non-active)
of the aquatic fouling organisms by grasping the life
mode of the aquatic fouling organisms in accordance
with the season, weather, sites or months.
